An inverter circuit for converting direct current (DC) to alternating current (AC) includes multiple semiconductor switching elements. If the switching elements are heated beyond maximum rated temperatures, the switching elements are destroyed. Therefore, typically, an inverter apparatus for driving the inverter circuit detects temperatures of the switching elements and performs an overheat protection for protecting the switching elements from overheating, based on the detected temperatures.
For example, an inverter apparatus disclosed in JP-2001-169401A detects the temperatures of all the switching elements in the inverter circuit and controls output current of the inverter circuit based on the maximum temperature. The inverter apparatus needs many temperature sensors and a large space for the temperature sensors. Therefore, the size and manufacturing cost of the inverter apparatus are increased.